第1部分:微合金钢的应变时效行为使用各种应变、时效和应力消除循环研究了五种微合金钢的应变时效行为。所研究的材料为压力容器钢ASTM A737 B级和A737 C级，以及结构钢ASTM A588 A级、A588 B级和ASTM A572 50级2型。A737 B级和C级钢在正火条件下进行试验，而A588 A级和B级钢以及A572 50 2型钢在轧制和正火条件下进行试验。这些钢在2%、5%或10%的张力下进行冷应变，并在260或370°C（500或700°F）下时效10小时。在620°C（1150°F）条件下，对应变和老化试样进行2小时和10小时的应力消除。测量了经处理、应变、时效和应力消除钢的横向力学性能。研究结果表明，所有钢材都对应变时效敏感，因为它们的强度增加，韧性降低。 对于5%到10%的冷应变，34J（25 ft-lb）夏比冲击转变温度的平均增加为38℃（68℉）。620°C（1150°F）下的应变后应力消除并没有将韧性恢复到其原始水平，只是将转变温度平均降低了5°C（8°F）。由于横向定向试验，结构等级、A588等级A和B以及A572等级50的应变时效转变温度等于或高于环境温度。屈服强度和拉伸强度随着应变和老化而增加。应力消除确实再次降低了强度，但没有达到其原始值。应变时效的程度对先前的应变量敏感，但对应变或时效温度的试样取向不敏感。延长应力消除周期并没有导致韧性的任何改善。老化本身并不会导致转变温度的显著升高，但对某些材料而言，应力消除处理本身却会导致转变温度的显著升高。 即使在应力消除之后，应变时效也会导致转变温度的大幅度变化，无论何时考虑这些材料的冷成型，尤其是在结构等级中，都必须考虑到这一点。第2部分:ASTM A737 B级和C级微合金钢的断裂韧性行为本程序中测试的材料被视为微合金钢，一类低合金高强度钢，利用相对低的碳含量和精细分散的碳化物提供强度和韧性。这种类型的钢已根据多个规范用于管道和结构应用，并已纳入ASTM压力容器板规范，如A734、A735和A737。这些钢的屈服强度水平比普通碳锰钢（A515或A516）高24%至100%以上（取决于等级）。其最低抗拉强度与最高强度碳钢等级相同，可能高出21%。 此外，这些钢能够提供的夏比冲击转变温度水平远低于传统钢，这使得它们在需要低温韧性的应用中具有优越性。由于它们的碳含量通常较低，所以它们的焊接性也很好。由于这些一般特性，并为了进一步探索其在压力容器领域的潜力，压力容器研究委员会的材料部门通过其压力容器钢小组委员会对选定的此类钢进行了研究。PVRC的兴趣在于记录其强度和韧性的变化，将在下面讨论，并这样做的截面厚度足够大，以包括大多数压力容器服务。本文是PVRC研究报告。第3部分:ASTM A737 B级和C级微合金钢焊接件的断裂行为A737 B级和C级钢焊接件的强度和断裂韧度是在as- 焊接条件和焊后热处理。这两种母材以2.8 kJ/mm（70 kJ/in.）的热输入进行埋弧焊使用Armco W-19（3.5 Ni）填充金属和Linde 709-5助焊剂。贱金属为76毫米（3.0英寸）（A737 C级）和102毫米（4.0英寸）厚度为（A737 B级）且采用“K”形多道焊缝设计，为韧性试验提供了相对平直的热影响区。以593°C（1100°F）下0、2和10小时的焊后热处理作为试验变量。第4部分:ASTM A737 B级和C级微合金钢的长时间应力消除效应进行了一项实验计划，以研究在620°C（1150°F）温度下的应力消除热处理对碳锰铌钢（ASTM A737 B级）和碳锰钒氮钢（A737 C级）在两种热处理条件下的机械性能的影响，正火、淬火和回火。 在620°C下，10小时或更短的应力消除处理时间内，韧性仅发生轻微变化。在更长的时间内，30小时或更长的时间内，正火钢中观察到应力消除脆化，其程度取决于时间和温度。脆化的特点是:（1）非C曲线行为，（2）无晶间解理断裂，（3）先前的热处理没有一致的效果，（4）韧性没有低谷，（5）无二次硬化。从这些观察结果可以得出结论，A737钢中观察到的脆化既不是典型的回火脆化，也不是一致的碳化物形成。发现韧性与碳化物厚度之间存在良好的相关性。所有这些结果表明，脆化机理为碳化物粗化。对于A737 C级，在620°C（1150°F）下进行长达10小时的应力消除处理时，强度变化很小，但对于A737 B级，在1小时后观察到强度变化。 当应力消除时间延长至100小时及以上时，屈服强度和抗拉强度明显降低。

Part 1: The Strain Aging Behavior of Microalloyed SteelsThe strain aging behavior of five microalloyed steels was studied using a variety of straining, aging and stress relieving cycles. The materials studied were pressure vessel steels ASTM A737 Grade B and A737 Grade C, and structural steels ASTM A588 Grade A, A588 Grade B and ASTM A572 Grade 50, Type 2. The A737 Grade B and Grade C steels were tested in the normalized condition while the A588 Grades A and B and the A572 Grade 50 Type 2 steel were tested in both the as-rolled and normalized condition. The steels were cold strained in tension 2, 5 or 10% and were aged at 260 or 370°C (500 or 700°F) for 10 hr. Strained and aged specimens were stress relieved for 2 and 10 hr at 620°C (1150°F). Transverse mechanical properties were measured for the as treated, strained, aged and stress relieved steels.The results of the study showed that all of the steels were sensitive to strain aging by increases in strength and losses in toughness. The average increase in 34J (25 ft-lb) Charpy impact transition temperature for 5 to 10% cold strain was 38°C (68°F). Post-strain stress relief at 620°C (1150°F) did not restore toughness to its original level, only reducing the transition temperatures by an average of 5°C (8°-F). Because of the transverse orientation tests, the strain-aged transition temperatures for the structural grades, A588 Grades A and B and A572 Grade 50 were equal to or above ambient temperature. Yield and tensile strength increased with straining and aging. Stress relief did reduce the strength again but not to its original values.The extent of strain aging was sensitive to the amount of prior strain but not to specimen orientation to straining or aging temperature. Extended stress relief cycles did not result in any improvement in toughness. Aging alone did not result in a significant increase in transition temperature but stress relief treatments alone did for some materials.Extensive shifts in transition temperature were produced by strain aging even after stress relief and this must be taken into account whenever the cold forming of these materials is considered, especially in the structural grades.Part 2: The Fracture Toughness Behavior of ASTM A737 Grade B and Grade C Microalloyed Pressure Vessel SteelsThe materials tested in this program are considered microalloyed steels, a class of low-alloy high-strength steels that utilizes relatively low carbon content and finely dispersed carbides to provide strength and toughness. This type of steel has been used for piping and structural applications under several specifications and has been incorporated into ASTM pressure vessel plate specifications such as A734, A735 and A737. The yield strength levels of these steels exceed those of normal carbon-manganese steels (A515 or A516) by 24% to over 100% (depending on grade). Their lowest tensile strengths are the same as the highest strength carbon steel grades and may be 21% higher. In addition, the Charpy impact transition temperature levels the steels are able to provide are much lower than conventional steels, which makes them superior in applications requiring low temperature toughness. Due to their generally low carbon content, their weldability is also good.Because of these general characteristics, and to explore further their potential in the pressure vessel field, the Materials Division of the Pressure Vessel Research Committee, through its Pressure Vessel Steels Subcommittee instituted a study of selected steels of this type. The interest of the PVRC was to document their strength and toughness in the variations to be discussed below, and to do so in section thicknesses great enough to include most pressure vessel service. This paper is a report of the PVRC study.Part 3: The Fracture Behavior of ASTM A737 Grade B and Grade C Microalloyed Steel WeldmentsThe strength and fracture toughness of weldments of A737 Grades B and C steel were determined over a range of temperatures both in the as-welded condition and after post-weld heat treatment. The two base metals were submerged arc welded at a heat input of 2.8 kJ/mm (70 kJ/in.) using Armco W-19 (3.5 Ni) filler metal and Linde 709-5 flux. The base metals were 76 mm (3.0 in.) (A737 Grade C) and 102 mm (4.0 in.) (A737 Grade B) in thickness and a "K" configuration multipass weld joint design was used to provide a relatively straight heat-affected zone for toughness testing. Post weld heat treatment at 593°C (1100°F) for 0, 2 and 10 hr was used as a test variable.Part 4: Long Time Stress Relief Effects In ASTM A737 Grade B and Grade C Microalloyed SteelsAn experimental program was conducted to investigate the effect of stress relief heat treatment at 620°C (1150°F) on the mechanical properties of a carbon-manganese-niobium steel (ASTM A737 Grade B) and a carbon-manganesevanadium-nitrogen steel (A737 Grade C) in two conditions of heat treatment, normalized, and quenched and tempered. Only modest changes in toughness occurred for stress relief treatment times of 10 hr or less at 620°C. For longer times, 30 hr or more, stress relief embrittlement was observed in the normalized steels, the extent being time and temperature dependent. The embrittlement was characterized by (1) non C-curve behavior, (2) no intergranular cleavage fracture, (3) no consistent effect of prior heat treatment, (4) no trough in toughness, and (5) no secondary hardening. From these observations the conclusion was made that neither classical temper embrittlement nor coherent carbide formation is responsible for the embrittlement observed in the A737 steels. A good correlation between toughness and the carbide thickness was found. From all of these results, the embrittlement mechanism was concluded to be carbide coarsening.Strength changes were small for stress relief treatments of up to 10 hr at 620°C (1150°F) for the A737 Grade C, but were observed after 1 hr for the A737 Grade B. There were distinct decreases in yield and tensile strength for stress relief times that extended to 100 hr and beyond.