Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
  • C21D8/10—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of tubular bodies
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/20—Ferrous alloys, e.g. steel alloys containing chromium with copper
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/22—Ferrous alloys, e.g. steel alloys containing chromium with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/24—Ferrous alloys, e.g. steel alloys containing chromium with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/28—Ferrous alloys, e.g. steel alloys containing chromium with titanium or zirconium

Definitions

• the present invention relates to low carbon alloy steel tubes having ultra high strength and excellent toughness at low temperature and also to a method of manufacturing such a steel tube.
• the steel tube is particularly suitable for making components for containers for automotive restraint systems, an example of which is an automotive airbag inflator.
• Japanese Publication No. 10-140249 [Application date Nov. 5, 1996] and Japanese Publication No. 10-140283 [Application date Nov. 12, 1996] illustrate in general terms steel chemistry considered useful for an automotive airbag inflator. These documents mention as a final condition the absence of heat treatment, a stress relieving, and a normalizing or a quenching and tempering. These publications do not mention the possibility of just a quenching as a heat treatment step. No mechanical properties are mentioned in the claims. In the various examples, only in example #21 is the steel quenched and tempered, but the reported UTS is only 686 MPa (99 ksi).
• Japanese Publication No. 2001-49343 [Application date Oct. 8, 1999] is said to address only steels for use in making electric-resistance-welded tubes (the ERW process).
• the claims specify various aspects of the ERW process and an optional heat treatment for a normalizing or quench and temper, an optional ulterior cold drawing, an optional ulterior heat treatment (normalizing or quench and temper).
• This document addresses only two different, very general steel chemistry, one being a low carbon steel, the other noting common limits in various alloying elements. This document does not suggest the possibility of just a quenching heat treatment.
• Various examples are given for a quench and temper material, but mechanical properties obtained are relatively low. The maximum result achieved is 852 MPa (123 ksi) in the quench and temper test #18.
• Airbag inflators for vehicle occupant restraint systems are required to meet strict structural and functional standards. Therefore, strict procedures and tolerances are imposed on the manufacturing process. While field experience indicates that the industry has been successful in meeting past structural and functional standards, improved and/or new properties are necessary to satisfy the evolving requirements, while at the same time a continuous reduction in the manufacturing costs is also important.
• Airbags or supplemental restraint systems are an important safety feature in many of today's vehicles.
• air bag systems were of the type employing explosive chemicals, but they are expensive, and due to environmental and recycling problems, in recent years, a new type of inflator has been developed using an accumulator made of a steel tube filled with argon gas or the like, and this type is increasingly being used.
• the above-mentioned accumulator is a container which at normal times maintains the gas or the like at a high pressure which is blown into an airbag at the time of the collision of an automobile, in a single or multiple stage burst. Accordingly, a steel tube used as such an accumulator is to receive a stress at a high strain rate in an extremely short period of time. Therefore, compared with a simple structure such as an ordinary pressure cylinder, the above-described steel tube is required to have superior dimensional accuracy, excellent workability, and weldability, and above all must have high strength, toughness, and excellent resistance to bursting. Dimensional accuracy also is important to ensure a very precise volume of gas will blow into the airbag.
• Cold forming properties are very important in tubular members used to manufacture accumulators since they are formed to final shape after the tube is manufactured. Different shapes depending on the vessel configuration shall be obtained by cold forming. It is crucial to obtain pressure vessels without cracks and superficial defects after cold forming. Moreover, it is also vital to have very good toughness even at low temperatures after cold forming.
• the steels disclosed herein have very good weldability, and do not require, for air bag accumulator applications, either a preheating prior to welding, or a post weld heat treatment.
• the carbon equivalent, as defined by the formula, Ceq-% C+% Mn/6+(% Cr+% Mo+% V)/5+(% Ni+% Cu)/15 should be less than about 0.63% in order to obtain the required weldability. As Ceq diminishes, weldability improves, hi the preferred embodiment of this invention, the carbon equivalent as defined above should be less than about 0.60%, preferably less than about 0.56%, and most preferably less than about 0.52%, or even less than about 0.48%, in order to better guarantee weldability.
• a cold-drawn tube made according to the present invention is cut to length and then cold formed using different known technologies (such as crimping, swaging, or the like) in order to obtain the desired shape.
• a welded tube could be used.
• an end cap and a diffuser are welded to each end of the container by any suitable technology such as friction welding, gas tungsten arc welding or laser welding.
• the inflators are tested to assure that they retain their structural integrity during airbag deployment.
• One of such tests is the so-called burst test. This is a destructive-type test in which a canister is subjected to internal pressures significantly higher than those expected during normal operational use, i.e., airbag deployment. In this test, the inflator is subjected to increasing internal pressures until rupture occurs.
• the present invention first relates to certain novel low carbon alloy steels suitable for cold forming having more than high tensile strength (UTS 145 ksi minimum) and preferably ultra high tensile strength (UTS 160 ksi minimum and possibly 175 ksi or 220 ksi), and, consequently, a very high burst pressure.
• the steel has excellent toughness at low temperature, with guaranteed ductile behavior at -60 0 C, i.e., a ductile-to-brittle transition temperature (DBTT) below -60 0 C, and possibly as low as -100 0 C.
• DBTT ductile-to-brittle transition temperature
• the present invention also relates to a process of manufacturing such a steel tube which essentially comprises a novel rapid induction austenizing/high speed quench/no temper technique.
• a novel rapid induction austenizing/high speed quench/no temper technique there is an extremely rapid induction austenizing with an ultra fast water quenching step that eliminates any tempering step, so as to create a low carbon alloy steel tube that also is suitable for cold forming having ultra high tensile strength (UTS 145 ksi minimum and up to220 ksi), and, consequently, a very high burst pressure.
• UTS 145 ksi minimum and up to220 ksi ultra high tensile strength
• the steel has excellent toughness at low temperature, with guaranteed ductile behavior at -60 °C, i.e., a ductile-to-brittle transition temperature (DBTT) that is below -60° C, and possibly even as low as -100 0 C.
• DBTT ductile-to-brittle transition temperature
• the material of the present invention has particular utility in components for containers for automotive restraint system components, an example of which is an automotive airbag inflator.
• the chemistry used to create each of the steels disclosed herein is novel, hereafter will be identified as Steel A, Steel B, Steel C, Steel D and Steel E, with the compositions for each being summarized in the following Table I:
• FIG. I is a core microstructure for a high speed quench on Steel E
• FIG. II shows burst tests at -60 C for a high speed quench on Steel E.
• FIG. Ill shows microstructure for a normal quench on Steel E
• Figure IV shows a high speed quench core microstructure on Steel D
• Figure V shows burst test at -60 C for a high speed quench on Steel D.
• Figure VI shows micro-structure for a normal quench on Steel D
• the present invention relates to steel tubing to be used for stored gas inflator pressure vessels. More particularly, the present invention relates to a low carbon ultra high strength steel grade for seamless pressure vessel applications with guaranteed ductile behavior at -60 0 C, i.e., a ductile-to-brittle transition temperature below -60 0 C, and possibly even as low as -100 °.
• the present invention relates to a chemical composition and a manufacturing process to obtain a seamless steel tubing to be used to manufacture an inflator.
• a schematic illustration of a method of producing the seamless low carbon ultra high strength steel could be as follows:
• One of the main objectives of the steel-making process is to refine the iron by removal of carbon, silicon, sulfur, phosphorous, and manganese, hi particular, sulfur and phosphorous are prejudicial for the steel because they worsen the mechanical properties of the material.
• Ladle metallurgy is used before or after basic processing to perform specific purification steps that allow faster processing in the basic steel making operation.
• the steel-making process is performed under an extreme clean practice in order to obtain a very low sulfur and phosphorous content, which in turn is crucial for obtaining the high toughness required by the product. Accordingly, the objective of an inclusion level of 2 or less —thin series--, and level 1 or less —heavy series--, under the guidelines of ASTM E45 Standard- Worst Field Method (Method A) has been imposed.
• the maximum microinclusion content as measured according to the above-mentioned Standard should be:
• the extreme clean practice allows obtaining oversize inclusion content with 30 ⁇ m or less in size. These inclusion contents are obtained limiting the total oxygen content to 20 ppm.
• C is an element that inexpensively raises the strength of the steel, but if its content is less than 0.06% it is difficult to obtain the desired strength. On the other hand, if the steel has a C content greater than 0.18%, then cold workability, weldability, and toughness decrease. Therefore, the C content range is 0.06% to 0.18%. A preferred range for the C content is 0.07% to 0.12%, and an even more preferred range is 0.10 to 0.12%.
• Mn is an element which is effective in increasing the hardenability of the steel, and therefore it increases strength and toughness. If it content is less than 0.3% it is difficult to obtain the desired strength, whereas if it exceeds 1.5%, then banding structures become marked, and toughness decreases. Accordingly, the Mn content is 0.3% to 1.5%, with a preferred Mn range of 0.60 to 1.40%.
• Si is an element which has a deoxidizing effect during steel making process and also raises the strength of the steel. If Si content is less than 0.05%, the steel is susceptible to oxidation, on the other hand if it exceeds 0.50%, then both toughness and workability decrease. Therefore, the Si content is 0.05% to 0.5%., and a preferred Si range of 0.05% to 0.40%.
• S is an element that causes the toughness of the steel to decrease. Accordingly, the S content is limited to 0.015 % maximum. A preferred maximum value is 0.010%
• P is an element that causes the toughness of the steel to decrease. Accordingly, the P content is limited to 0.025% maximum. A preferred maximum value is 0.02%,
• Ni is an element that increases the strength and toughness of the steel, but it is very costly, therefore for cost reasons Ni is limited to 0.70% maximum. A preferred maximum value is 0.50%.
• Cr is an element which is effective in increasing the strength, toughness, and corrosion resistance of the steel. If it exceeds 1% the toughness at the welding zones decreases markedly. Accordingly, the Cr content is limited to 1.0% maximum, and a preferred Cr maximum content is 0.80%,
• Mo is an element which is effective in increasing the strength of the steel and contributes to retard the softening during tempering, but it is very costly . Accordingly, the Mo content is limited to 0.7% maximum, and a preferred Mo maximum content is 0.50%
• V is an element which is effective in increasing the strength of the steel, even if added in small amounts, and allows to retard the softening during tempering.
• this ferroalloy is expensive, forcing the necessity to lower the maximum content. Therefore, V is limited to 0.3% maximum, with a preferred maximum of 0.20%
• Residual elements in a single ladle of steel used to produce tubing or chambers shall be:
• the next step is the steel casting to produce a solid steel bar capable of being pierced and rolled to form a seamless steel tube.
• the steel is cast in the steel shop into a round solid billet, having a uniform diameter along the steel axis.
• the solid cylindrical billet of ultra high clean steel is heated to a temperature of about 1200 0 C. to 1300 0 C, and at this point undergoes the rolling mill process.
• the billet is heated to a temperature of about 1250 0 C, and then passed through the rolling mill.
• the billet is pierced, preferably utilizing the known Manessmann process, and subsequently the outside diameter and wall thickness are substantially reduced while the length is substantially increased during hot rolling. For example, a 148 mm outside diameter solid bar is hot rolled into a 48.3 mm outside diameter hot- rolled tube, with a wall thickness of 3.25 mm.
• the cross-sectional area reduction measured as the ratio of the cross-sectional area of the solid billet to the cross-sectional area of the hot-rolled tube, is important in order to obtain a refined microstructure, necessary to get the desired mechanical properties. Therefore, the minimum cross-sectional area reduction is about 15:1, with preferred and most preferred minimum cross-sectional area reductions of about 20:1 and about 25:1, respectively.
• the seamless hot-rolled tube of ultra high clean steel so manufactured is cooled to room temperature.
• the seamless hot-rolled tube of ultra high clean steel so manufactured has an approximately uniform wall thickness, both circumferentially around the tube and longitudinally along the tube axis.
• the hot-rolled tube is then passed through different finishing steps, for example cut in length into 2 to 4 pieces, and its ends cropped, straightened at known rotary straightening equipment if necessary, and non-destructively tested by one or more of the different known techniques, like electromagnetic testing or ultrasound testing.
• each piece of hot-rolled tube is then properly conditioned for cold drawing.
• This conditioning includes pickling by immersion in acid solution, and applying an appropriate layer of lubricants, like the known zinc phosphate and sodium estearathe combination, or reactive oil.
• the seamless tube is cold drawn, pulling it through an external die that has a diameter smaller than the outside diameter of the tube being drawn.
• the internal surface of the tube is also supported by an internal mandrel anchored to one end of a rod, so that the mandrel remains close to the die during drawing. This drawing operation is performed without the necessity of previously heating the tube above room temperature.
• the seamless tube is so cold drawn at least once, each pass reducing both the outside diameter and the wall thickness of the tube.
• the cold-drawn steel tube so manufactured has a uniform outside diameter along the tube axis, and a uniform wall thickness both circurnferentially around the tube and longitudinally along the tube axis.
• the so cold-drawn tube has an outside diameter preferably between 10 and 70 mm, and a wall thickness preferably from 1 to 4 mm.
• the cold-drawn tube is then heat treated in an austenizing furnace at a temperature of at least the upper austenizing temperature, or Ac3 (which, for the specific chemistry disclosed herein, is about 880 0 C), but preferably above about 920 0 C. and below about 1050 0 C.
• This maximum austenizing temperature is imposed in order to avoid grain coarsening.
• This process can be performed either in a fuel furnace or in an induction-type furnace, but preferably in the latter.
• the transit time in the furnace is strongly dependent on the type of furnace utilized. It has been found that the high surface quality required by this application is better obtained if an induction type furnace is utilized. This is due to the nature of the induction process, in which very short transit times are involved, precluding oxidation to occur.
• the austenizing heating rate is at least about 100 0 C. per second, but more preferably at least about 200 0 C. per second.
• the extremely high heating rate and, as a consequence, very low heating times, are important for obtaining a very fine grain microstructure, which in turn guarantees the required mechanical properties.
• an appropriate filling factor defined as the ratio of the round area defined by the outer diameter of the tube to the round area defined by the coil inside diameter of the induction furnace, is important for obtaining the required high heating rates.
• the minimum filling factor is about 0.16, and a preferred minimum filling factor is about 0.36.
• the tube is quenched by means of an appropriate quenching fluid.
• the quenching fluid is preferably water or water-based quenching solution.
• the tube temperature drops rapidly to ambient temperature, preferably at a rate of at least about 100 0 C. per second, more preferably at a rate of at least about 200 0 C. per second. This extremely high cooling rate is crucial for obtaining a complete microstracture transformation.
• the steel tube is then tempered with an appropriate temperature and cycle time, at a temperature below AcI.
• the tempering temperature is between about 400-600 0 C, and more preferably between about 450-550 0 C.
• the tempering temperature may be between 200 0 C to 600 °C and more preferably between 250°C to 55O 0 C.
• the soaking time shall be long enough to guarantee a very good temperature homogeneity, but if it is too long, the desired mechanical properties are not obtained.
• This tempering step is performed preferably in a protective reducing or neutral atmosphere to avoid decarburizing and/or oxidation of the tube.
• the tempering step is eliminated and only a high speed quench using water or water based solutions , as described above, is employed. hi order to achieve a high speed quench, the following equipment is preferred, but not required.
• a Quenching line with a full capacity of 2200 kg per hour follows an induction furnace with a maximum power of inductor settled at 500 Kw.
• a head quencher employs 42 lines with 12 nozzles on each line. Water quenching flow is adjusted into a range of 10 to 60 m3 per hour, and the advance speed of the tube is controlled from
• pinch rollers are set up to produce a rotation over the tube.
• the ultra high strength steel tube so manufactured is passed through different finishing steps, straightened at known rotary straightening equipment, and non- destructively tested by one or more of the different known techniques.
• tubes should be tested by means of both known ultrasound and electromagnetic techniques.
• the tubing after heat treatment can be chemically processed to obtain a tube with a desirable appearance and very low surface roughness.
• the tube could be pickled in a sulfuric acid and hydrochloric acid solution, phosphated using zinc phosphate, and oiled using a petroleum-based oil, a water-based oil, or a mineral oil.
• a steel tube obtained by the first or second described methods have the following minimum mechanical properties:
• the yield strength, tensile strength, and elongation are to be performed according to the procedures described in the Standards ASTM E8.
• a full size specimen for evaluating the whole tubular section is preferred.
• the prior (sometimes referred to as former) austenitic grain size shall be preferably 7 or finer, and more preferably 9 or finer, as measured according to ASTM E-112 Standard. This is accomplished thanks to the extremely short heating cycle during austenitizing.
• the steel tube obtained by the described method shall have the stated properties in order to comply with the requirements stated for the invention.
• the demand of the industry is continuously pushing roughness requirements to lower values.
• the present invention has a good visual appearance, with, for example, a surface finish of the finished tubing of 3.2 microns maximum, both at the external and internal surfaces. This requirement is obtained through cold drawing, short austenizing times, reducing or neutral atmosphere tempering, and an adequate surface chemical conditioning at different steps of the process.
• a hydroburst pressure test shall be performed by sealing the ends of the tube section, for example, by welding flat steel plates to the ends of the tube. It is important that a 300 mm tube section remains constraint free so that full hoop stress can develop.
• the pressurization of the tube section shall be performed by pumping oil, water, alcohol or a mixture of them.
• the burst test pressure requirement depends on the tube size.
• the ultra high strength steel seamless tube has a guaranteed ductile behavior at -60 0 C.
• Tests performed on the samples produced show that this grade has a guaranteed ductile behavior at -60 0 C, with a ductile-to-brittle transition temperature below -60 0 C.
• the inventors have found that a far more representative validation test is the burst test, performed both at ambient and at low temperature, instead of Charpy impact test (according to ASTM E23). This is due to the fact that relatively thin wall thicknesses and small outside diameter in these products are employed, therefore no standard ASTM specimen for Charpy impact test can be machined from the tube in the transverse direction. Moreover, in order to get this subsize Charpy impact probe, a flattening deformation has to be applied to a curved tube probe. This has a sensible effect on the steel mechanical properties, in particular the impact strength. Therefore, no representative impact test is obtained with this procedure.
• novel Steels A 5 B, C, D and E are alternative steels that were analyzed using the preferred method, wherein a very fast induction furnace austenizing with a high speed quench was used instead of adding a tempering step.
• control testing was done with certain of these novel steels wherein less than a high speed quench, i.e, a normal quenching process was employed or a tempering step, as described hereinbefore, was employed, the tests showed significantly poorer characteristics.
• Figure III presents the core structures for Steel E using normal quenching process. Some ferrite structure is observed along the wall thickness.
• Steel D was discovered to be very promising because of the high performance to cost value it presented.
• Steel D was selected to manufacture tubing according to the preferred method. Measured chemical composition of samples of Steel D that were used for high speed quench tests were as follows:
• Figure IV shows that a high speed quench Steel D microstructure that presents Martensite at 100% and a completely quenched transformation. Likewise, burst tests at low temperature (- 60° C) were performed in order to observe the behavior and type of crack.
• Figure V shows tested burst samples for Steel D. Both presented a ductile behavior.
• Figure VI presents the core structures for Steel D using normal quenching process.
• Steel B was selected to manufacture tubing according to the preferred method. Measured chemical composition of samples of Steel B that were used for high speed quench tests were as follows:
• a tempering heat treatment was conducted at 580 °C for total time of 15 minutes.
• the UTS average was 116 Ksi (805 MPa), which do not meet the expected values

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