TECH SPOTLIGHT This HSLA plate meets the typical mechanical properties, has excellent weldability, and offers significant savings.
Fig. 1 — HSLA-100 starting material during initial forge reduction.
Exploring Expl oring HSLA steel forging forgingss Mark Royer* Lenape Forged Products Corp. West Chester, Pennsylvania
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or several decades, HY-80 and HY-100 forgings have been utilized for U.S. Navy ship applica-
tions. Although these grades have the requisite strength and toughness at low temperatures, they are susceptible to hydrogen-induced cracking after welding. To eliminate cracking, both grades grade s require a weld preheat prehe at of approximately 400 to 550ºF, 550ºF, depending on section thickness. Since this preheat adds considerable expense in production, a lower-cost alternative would be advantageous. Since the mid-1980’s, high-strength low-alloy (HSLA) steel plate has been approved as an alternative material to HY-80/HY-100. HY-80/HY-100. This HSLA plate meets the typical mechanical properties, excelle nt excellent weldability weldability, , and offers has significant savings due to reduced material, labor, energy, and inspection costs. In fact, it has been conservatively estimated that through * Member of ASM International
2001, over $100 million had been several elemental differences, but saved by replacing HY HY-80/HY -80/HY-100 -100 copper and carbon are of particular with HSLA HSLA steel. Because Because HSLA HSLA in note. For the HSLA-100, the carbon the form of plate has proven to be a content is much lower than the HYsuitable replacement material, the 100 material. On the other hand, potential for HSLA HSLA forgings in lieu copper is significantly higher in the of their HY-80/HY-100 HY-80/HY-100 counterparts counterp arts HSLA-100. Although this element is is evident. merely a residual for HY HY-100, -100, copper To evaluate the feasibility using is an intentional alloying element for HSLA, Lenape Forged Products was HSLA-100, and plays a vital role in contracted to produce cylindrical heat treatment. forgings of two sizes: Both carbon and copper speak to • One was nominally 30.30 inches the fundamental distinction between OD x 15.00 inches ID x 6.88 inches these grades of steel. While HY-100 long. achieves its strengthening by a • The other was approxi0.4 mately 37.41 inches OD x 22.40 inches ID x 6.66 inches long. Zone 3, • Disk forgings 34.38 inches % 0.3 Zone 2, Difficult to . OD x 6.38 inches thick were also t Weldable weld w , t produced. n e All of these products were t n 0.2 o HY-100 manufactured from a 31-inch c n o HSLA-100 starting ingot. The b r a C 0.1
chemistry is a modified MIL-S24645, Comp. III, as shown in Table 1. 1.
Zone 1, Easily weldable 0.3
0.4
0.5
HSLA-100 0.6
0.7
0.8
Carbon equivalent, CE Carbon and copper Chemistries of the alloys show Fig. 2 — Graville Diagram
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martensitic transformation during quenching and tempering, HSLA100 is strengthened by quenching and subsequent aging of copper precipitates. Because these materials
achieve strengthening by different mechanisms, they also require different processing to develop the necessary mechanical properties. Both HY-80 and HY-100 require a nor-
Table 1 — Comparison of chemistries Element Carbon Manganese Phosphorus
Sulfur Silicon Nickel Chromium Molybdenum Nitrogen Arsenic Vanadium Titanium Copper Columbium Aluminum Tin 0.03 Antimony Carbon equivalent, CE*
HSLA-100, comp. III 0.02 — 0.04 0.75 — 1.05 0.015 max
HY-100 0.12 — 0.20 0.10 — 0.40 0.015
0.002 max 0.40 max 3.35—3.85 0.45 — 0.75 0.55 — 0.65 INFO ONLY 0.025 max 0.008 max 0.003 max 1.15 — 1.75 0.02 — 0.06 0.03 0.030 0.025 0.81
0.004 0.15 — 0.35 2.75 — 3.50 1.35 — 1.80 0.30 — 0.60 NA 0.025 0.03 0.02 0.25 NA NA — 0.025 0.81
*CE (carbon equivalent) in this case is defined as C + (Mn + Si)/6 + (Cr + Mo + V)/5 + (Ni + Cu)/15. Although CE is not a specific requirement, an approximate value (varying with individual heat chemistries) is provided for information purposes only.
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malize, quench, and temper, whereas HSLA-100 requires a double quench, followed by an aging heat treatment. Although not a specification requirement, as seen see n in Table Table 1, the approximate carbon equivalent (CE) is essentially the same for both materials. In general terms, as the CE increases, the likelihood for hydrogeninduced cracking also increases. However, if the combined effects of carbon content and CE are analyzed, it is evident that the relative weldabilities of HSLA-100 and HY-100 are markedly different. Referring to the Graville Diagram (Fig. 1), both materials have comparable carbon equivalents. equivalents . However, because becau se of its it s reduced reduce d carbon carbo n content, the HSLA-100 is considered easy to weld, while the higher carbon content of HY-100 results in material classified as difficult to weld. As mentioned earlier, the improved weldability of HSLA-100 translates into real production savings. Lower carbon content and reduced susceptibility to HIC indicate that the necessary weld preheat is considerably lower for HSLA. Depending on section thickness and the
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type of electrode, calculated preheats are anywhere from room temperature to 300ºF. With ever-increasing energy cost and thousands of tons of metal requiring preheat, millions of dollars in savings are clearly possible. Mechanical properties The Lenape project had even stricter specification requirements. Table 2 shows that higher hi gher impact energies and tighter restrictions were placed on both tensile and yield strength of HSLA 100. Although the elongation requirement was decreased by 2% and the test temperature for dynamic tears was increased by 20ºF 20ºF,, this this dema demanding nding combi combinati nation on of properties was of concern. A trial heat treatment treatment procedure was developed to evaluate final properties. Several test coupons were removed, then double waterquenched and aged at varying temperature and time conditions. In all cases, mechanical properties were met. Final test results did show complete compliance to the specified requirements. Of particular note is a dynamic tear value of 1289 ft-lb (average of three specimens). sp ecimens). Although the test temperature for dynamic tears was 20ºF warmer than specified for typical HY HY-80/HY-100, -80/HY-100, the high values suggest that the HSLA HSLAshould should easily meet 450 ft-lb ft-l b if tested at -40ºF. To summarize, preliminary test results on HSLA-100 forgings indicate that a further investigation into the viability of this grade as a ship building buildin g materia materiall is warran warranted. ted. Even though the raw material and production heat-treatment costs are similar, HSLA-100 does have a clear advantage with its lower preheat temperature. The ability to meet mechanical property requirements, plus the fact that the forgeability of HSLA-100 is comparable to that of any carbon or alloy steel, make this grade a distinct possibility for applications such as guide rails, pressure vessels, valve bodies bod ies,, ins insert erts, s, and many oth other er forged components. Significant work remains to certify HSLA-100 forgings, but the economic benefits seem to far outweigh the cost associated with first article testing.
Table 2 — Typical Typical minimum min imum mechanical mechani cal properties proper ties Min. required for HY-100 No mi mini nimu mum m re requ quir ired ed — test result for informational purposes only Longitudinal tensile yield strength, 100 to 115 0.2% offset, ksi Longitudinal elong. in 2 in., % 18 Longitudinal red. of area, % 50 Charpy V-notch, ft-lbs at 0ºF 60 Property Long Lo ngit itud udin inal al te tens nsile ile st stre reng ngth th,, ks ksii
Charpy Char py V-n -not otch ch,, ft ft-l -lb b at -1 -120 20ºF ºF Dynamic tear, ft-lb at -40ºF
35 (f (for or se sect ctio ion n si size zess > 6 in in.) .) 450 (for section sizes > 6 in.)
Min. required for HSLA-100 115 to 12 1255
100 to 110 16 50 80 60 650
For more information: Mark Royer is the Metallurgical Quality Manager at Lenape Forged Products Corp., West Chester, PA 19382; tel: 610/793-5090; royerm@
[email protected]; www.lenapeforge.com.
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