4140 Heat Treating Guide
Chemical Analysis C% Carbon 0.38 – 0.43 Mn% Manganese 0.75 – 1.00 max P% Phosphorus 0.035 max S% Sulfur 0.040 max Si% Silicon 0.20 – 0.35 Cr% Chromium 0.80 – 1.10 Mo% Molybdenum 0.15 – 0.25 General characteristics of 4140 Alloy Steel AISI or SAE 4130 grade is a low-alloy steel containing chromium and molybdenum as strengthening agents. Its chemical composition is as follows AISI/SAE 4140 grade is a versatile alloy with good atmospheric corrosion resistance and reasonable strength. It shows good overall combinations of strength, toughness, wear resistance and fatigue strength. Applications This alloy finds many applications as forgings for the aerospace and oil and gas industries, along with myriad uses in the automotive, agricultural and defense industries, Typical uses are forged gears and shafts, spindles, fixtures, jigs and collars. Forging Forging of this steel should be carried out between 2200 and 1650 º F (1200 and 900 º C).
The lower the finishing temperature from forging, the finer will be the grain size. This alloy should ideally not be forged below 1650 º F (900 º C) and should be slow cooled after forging.
Heat treatment Heat treatment is carried out after hot working to render the steel suitable for machining, and to meet the mechanical property ranges specified for the steel’s particular applications. Annealing Forgings of 4140 grade may be annealed by transferring the parts straight from the forging operation to a furnace held at a suitable temperature, between 1450 and 1550 º F (790 and 840 º C), holding for a suitable time then furnace cooling, forming a structure suitable for machining. This kind of treatment is best used for parts with simple shapes. If some areas of a forging will finish much colder than others then a uniform structure will not be obtained, in which case a spheroidizing anneal at around 1380 º F (750 º C) may be used. It is safe to say that experience alone will decide the best type of annealing treatment to be used prior to machining.
Normalizing This process is defined as heating a steel to a temperature above the ferrite to austenite transformation range and then cooling in air to a temperature well below this transformation range. This treatment may be carried out on forged products as a conditioning treatment prior to final heat treatment. Normalizing also serves to refine the structure of forgings that might have cooled non-uniformly from their forging operation. The nominal normalizing temperature for 4140 grade is 1600 º F (870 º C), but production experience may necessitate a temperature either 50 º F (10 º C) above or below this figure. In fact when forgings are normalized before, say, carburizing or hardening and tempering, the upper range of normalizing temperatures is used. When normalizing is the final heat treatment, the lower temperature range is used.
Hardening This heat treatment results in the formation of martensite after quenching, hence a great increase in hardness and tensile strength together with some loss of ductility. The steel should be austenitized at 1500 to 1550 º F (815 to 845 º C), the actual temperature being a function of chemical composition within the allowed range, section size and cooling method. Austenitizing should ensure all micro-constituents in the steel are transformed to austenite. Smaller sections of 4140 might be quenched in oil, heavier sections in water. Tempering is carried out to relieve stresses from the hardening process, but primarily to obtain the required mechanical properties. The actual tempering temperature will be chosen to meet the required properties, and in many cases will be a matter of trial and error.
Machinability The alloy is readily machinable. Simple shapes might be machined following a normalizing treatment, whereas more complex shapes will require annealing. At the carbon level of this grade, a structure of coarse lamellar pearlite to coarse spheroidite is normally optimum for machinability Weldability This grade has good weldability and may be welded using any commercial method. Parts should be preheated before welding at around 1100 º F (590 º C) and stress relieved after. Parts in the hardened and tempered condition should not be welded since mechanical properties will be adversely affected. Parts should be welded in the annealed condition only. Cold formability Any cold forming on this alloy should be carried out on material with a spheroidized structure.
Further heat treatment, hardening and tempering, is carried out where applicable on the finally formed part. To Send a Request for Quote, please or call 1.973.276.5000 or 1.800.600.9290 or fax 1.973.276.5050.
Guide To Ordering Heat Treating Services, How to Design Parts that will be Heat Treated, Steel Types Comparisons and Hardness Charts This “How to order heat treating services guide,” or “Processing,” is a guide for plant managers, purchasing agents, part designers, account representatives and machine operators, who can benefit in knowing how to order processing based on a customer’s desired parameters in the finished metal parts. By becoming familiar with this guide you will understand the effects that heat treating has on metal parts and be more knowledgeable of a heat treat process that will meet your specifications and quality specifications for simple tool steels, or for processing that must meet certifications for ISO, Nadcap, AMS, CQI-9 and AMS-H-6875-Dept.
Of Defense certifications. How to Work With a Heat Treater Your hardware is valuable to your business since it is the conduit for continuing relationships with your customers. We hope that this guide is informative to the point of increasing your interest in protecting your parts during the processing cycle. Please feel free to contact our Metallurgical Engineer or lab department if you need more information. Thank you, Peter Hushek, Phoenix Heat Treating President, 602-258-7751.
A heat treater is a specialist in the processing of metals. An experienced and reputable heat treater is able to diagnosis and recommend a preferred treatment for your metal parts only if he knows everything possible about the material that he will be working with. Therefore, it is important that the parts you send to a heat treater for processing include written information with the following details: Ordering heat treating Recommended Information to be Included with Your Purchase Orders 1.
Parts Identification for Packing and Shipping. Work submitted for heat treatment should be carefully identified with appropriate packing slip or purchase order. The number of parts for each part number or lot should be noted. Weights or similar data can be used where applicable. Cad Illustrations and Drawings.
All purchase orders for parts being processed the first time should include the drawings and all applicable specifications. If the drawings must be returned, note this on the PO, otherwise the drawings will be stored with your job order. Processing information pertinent to the heat treater should be noted, such as dimensional tolerances required, allowance required for stock removal, finishing operations that follow, and additional treatments or hardness tests. Material Designation. Specify the SAE or AISI material designation wherever possible. The material trade name or purchase specification can be substituted. For new or super alloys, include the manufacturer’s heat treating recommendations.
The use of general terms, such as “oil hardening tool steel” is incomplete information. Be more specific to prevent your metal from undergoing the wrong treatments. You need to know if your metal was cold formed in the mill, and if it was, make sure to tell the heat treater. Ask you supplier to contact the mill, if necessary to obtain this information.
Stress relieving may have to be preformed prior to the actual processing. Processing Information is Critical for Quality Heat Treating. The processing your parts should be described as best as possible with information you have available. If you are not sure about a type of process, call Phoenix Heat Treating at 602-258-7751, or another competent heat treating company, for information about a process that will meet the quality standards for the finished parts. We will help you write a processing order that will prevent unwanted results. General terms, such as “annealing,” should be more fully explained to avoid misinterpretation, especially when using a heat treating facility that is operating their equipment manually. Case hardening treatments should specify the method of reading the case depth (effective or total case depth), and the range allowed prior to grinding.
Case hardening depth needs to be specified in thousandths. Keep in mind that tighter tolerances for case depth are now achievable with heat treaters who provide automated heat treating. A “normal” case spread of ten-thousand’s can be set on automated equipment to not exceed a four-thousand’s case range. (More on this later in this outline). Thus you can be more specific on your hardening specifications.
Special operations or finishing treatments such as vapor blast, sand blast, plating, etc., should be specified. Treatments requiring other finishing processes, such as machining, should be carefully noted. If certified heat treating is required to meet certifications in the automotive, aerospace, military, medical, high-tech, etc., industries, a copy of the specification should accompany the work.
For error-free processing and guaranteed repeatability, it’s best to send your parts to a heat treat company that operates automated processing with sensor-control technology that documents the entire process. The automated logic-control systems used by Phoenix Heat Treating provide time-stamped, electronic records that prove the process was performed to meet ISO, Nadcap, AMS and CQI-9, Department of Defense certifications, and other specifications. Hardness Requirements. Hardness requirements should state the hardness test required, (Rockwell, Brinell, etc.), and range. For tool steels, a three-point hardness range is desirable, such as “Rockwell C 60-62.” Five to six points should be allowed on hardness below Rockwell C 50. Inspection locations should be noted. Critical areas in which hardness tests are not allowed should also be noted.
Stock removal allowed for preparing surfaces for hardness checking should be noted, if critical. Parts requiring heat treating to a specified tensile strength should be accompanied by tensile test specimens.
Conversion from tensile strength to hardness is not reliable and should be done only with your customer’s written approval. Tolerance Requirements. Specify the dimensional tolerances required after heat treatment. On critical work, it is recommended that you consult with an experienced heat treater prior to ordering processing. Finished surfaces should be carefully noted. Related Information for Ordering Heat Treating. Develop a close working relationship with a heat treater who can guarantee times, temperatures and atmospheres supported with repeatable performance.
Leading-edge automated heat treating eliminates the guess work involved in manually operated heat treating equipment. Processing is a very precise service that should be considered a critical finishing step in your metal fabrication. For that reason, a reputable, certified heat treater will encourage a working relationship with you to enhance your understanding of the processes and methods used; as well as allow the heat treater to get to know your company and your company’s needs and requirements.
The heat treater will help you better understand the processing steps and soak times required, and the related delivery schedules for the particular metal processing you are requesting. A reputable heat treater will want to know the ultimate utilization of your metal parts.
Involve Your Heat Treater Before Designing Parts We recommend that you ask your heat treater for input on finished part design prior to making part dies, instead of just relying on your own interpretation of a part that will be processed. Critical tolerances that have to meet deliverable specs can change through processing. Potential variables can be determined by a heat treating company’s METALLURGICAL ENGINEER who understands what happens to different metal types during processing. A turn-key heat treating company with an IN-HOUSE metallurgical engineer and INSPECTION LAB will provide you with critical specifications about the material your are working with. Knowing the chemistry and limitations of the material will enable you to produce higher quality parts that will not fail in service, and will allow you to provide a more informed service to your customers. A heat-treating company that offers full turn-key services will include lab service in your processing orders and will send it to third parties who are not familiar with your company. Know the Relationship Between Part Design and Heat Treating Heat treating of parts at some stage of production is most often a requirement.
For that reason, knowing how heat treating will affect part design is essential. Since the term heat treatment applies to many kinds of heat treat applications, we will limit this explanation to the quenching of steel that has been heated to it’s austenitizing temperature and held for a sufficient time to allow full solution. The designer’s role in this process is directed toward the production of a functional part requiring a minimum of manufacturing time and expense, as well as in machining, finishing, and knowing the appropriate heat treat process required to prevent movement in the work piece.
The heat treating industry, represented by the Metal Treating Institute, has developed an industry statement for heat treaters which recognizes that inherent problems in metal chemistry or part design can still make the job of properly heat treating a piece of metal very difficult, or impossible. Without knowing the origin of the metal and the utilization specifications, it would be risky to proceed with processing. The below information explains this more clearly. Knowing the source of stresses acting at various times prior to heat treating, or during the heat treating cycles is three-fold:. Stress created at the mill when the material was cold formed.
Stresses resulting from the mere application or removal of heat,. Stresses resulting from changes in the crystalline structures of the steel.
4140 Heat Treating Temperature
Simple cooling causes a metal part to shrink, but the structure change that developed hardness results in an increase in volume. As long as these changes occur uniformly throughout a piece, the resulting stress is minor. If the shape of a piece is such that a thin area cools faster and becomes hard while a thicker area is still cooling and becoming hard, the resulting stress can be great enough cause fissures or cracks. Comparisons of Improper and Proper Part Design The possibility of cracking can be minimized by modifying the design to balance the sections and thus improve the uniformity of cooling and hardening. 1-A and 1-B show how this can be accomplished without changing the die design.
Sharp or re-entrant angles act as stress concentration centers and if possible, should be avoided in part design. Cracks are very likely to develop in these corners during quenching, and a fillet in the design will help to minimize this risk.
4140 Heat Treating Guide
Fig 2-B shows a small, but important improvement over 2-A. Sometimes it is near impossible to design a part without incorporating adjoining light and heavy sections. While Fig 3-B is an improvement over Fig 3-A, there still is a risk for cracking where the shaft meets the base.
As well, the cylinder could warp during quenching because of two unbalanced masses. Before committing an unstable part design to manufacturing, you should discuss this with a metallurgical processing engineer. Fig 4-B illustrates design improvements that should be made in the Fig-A design. The corners of the keyways should be filleted to prevent cracks and the keyways should be cut opposite and at 90 degrees to each other to balance the piece so it will stay round where quenched. Fig 5-A illustrates a case of improper design in a double ended side-mill or spot-facer.
Each side of this tool has three teeth with the teeth placed opposite each other. This is an unbalanced design in the cross-section of the piece and is made more serious by a sharp corner at the base of the teeth. This tool design is most likely to crack at the junction between the light and heavy sections.
This condition may be corrected by staggering the teeth on opposite sides of the tool, and eliminating the sharp corner at the base of each tooth as shown in Fig 5-B. When cutting tools are designed, it is best to keep the hub and cutting edge as nearly the same thickness as possible. The heavy mass in the hub will tend to warp and buckle, if not crack, the lighter cutting section. If a radius is not provided at the base of gear teeth as in Fig 6-A, each corner will become a stress concentration point that can lead to cracks.
The design can be corrected by leaving generous fillets as shown in Fig 6-B. The design of the blanking die in Fig 7-A is not correct. Since the set-screw holes are in direct line with the sharp angels of the blanking section, they are likely to lead to a crack.
4140 Heat Treating Process
This condition also reduces the “land” in that area which makes the die unbalanced. Fig 7-B shows a better design. Fig 8-A and 8-B are longitudinal sections of cold drawing dies.
Stress set up in heat treatment and in service at the sharp corners of the small opening can easy cause spalling and flaking. This can be avoided by the use of a fillet as in 8-B. Thousands of dollars are spent each year on straightening of keywayed shafts. The shaft represented in Fig 9-A will have a great tendency to warp when quenched, whereas the shaft shown in Fig 9-B will stay more nearly straight because of the balanced section. If the keyways are impossible to add to shafts, the parts should be processed fluid bed or pit furnaces where they can be held in the vertical position. The preventative step needed in all of the above examples would be for the part designer to meet with an experienced metallurgical engineer prior to committing the design to production. This could save a lot of time and money and prevent parts from failing.
Facts About Metal Hardness and Heat Treating Hardness is the nearly universal measure of heat treat performance, because it has been found that a selected material processed to the required hardness performs well under certain loads. For example, spring steel at a hardness of Rockwell C45 performs well as a spring. Through experience it has been found that a hardness of Rc45 in spring steel is correlated with good toughness, resilience, and fatigue strength. The correlation is consistent, and Rc45 is accepted as a quality measure of heat treated springs, even though the hardness itself is not an important characteristic of a spring. For many parts where tensile strength, toughness, or fatigue strength may be the desired characteristics, these features have been correlated with hardness values. Most frequently, hardness is specified as the heat treat requirement only because hardness is easy to measure. The Brinell Metal Hardness Method The standard Brinell penetrator is a hardened steel ball (or carbide for use on hard materials), 10 mm in diameter.
On softer materials the ball is pressed into a previously flatted area of the test piece under a load of 500 kg. With the aid of a precision microscope having a built-in scale, the diameter of the hole is measured in millimeters.
Having this diameter, a table gives the corresponding Brinell number, commonly referred to as BHN, or Brinell Hardness Number. For harder work, the procedure is the same except that the load is larger in units of 500 kg. When using the Brinell number as a measure of hardness, it is most important that the load to be used in the test is specified along with the number itself; for example, 38 BHN (500 kg). The most commonly used load for soft materials is 500 kg and for hard materials, 3000 kg.
A small portion of the total Brinell scale is shown in the following table. Hole DIA Brinell Metal Hardness Number Mm 500 kg 1000 kg 1500 kg 2000 kg 2500 kg 3000 kg 3.00 69 138 208 276 346 415 3.05 67 134 201 267 334 401 3.10 65 129 194 258 324 388 3.15 62 125 188 250 313 375 4.00 38 76 115 152 191 229 4.05 37 74 112 148 186 223 4.10 36 72 109 145 181 217 4.15 35 71 106 141 177 212 Brinell machines come in a variety of models including hand operated, power operated, portable, manual, digital and direct reading machines for production work. Some of these use dead weight to apply the pressure to the ball, others employ hydraulic pressure. The Brinell test is easily and quickly made, and with a little practice the impression diameter can be read accurately. It is good practice to request that your heat treater’s lab use the average of two readings of the impression diameter made at right angles to each other.
Calibration of the machine should be done periodically with the use of metal test blocks of standard hardness. The Rockwell Hardness Method The Rockwell method of measuring hardness is a system consisting of several different kinds of penetrators that may be applied to test pieces under a variety of loads. The various combinations of penetrators and loads determine a number of Rockwell hardness scales – each combination of load and penetrator being designated by a letter. The system is divided into two divisions, one of which, called “superficial”, employs very light loads and is intended mainly for use on thin work or work with a very thin case. Some Rockwell testing machines are adapted for both the standard and superficial scales and the testing equipment may be manual requiring an operator, or automated.
Factory service manual for 1992 sentra. Many leading heat treating companies will use both methods of testing hardness.