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Halilbeyli OSB Mah. Nif Cad. No:20
Kemalpaşa / İzmir, Türkiye

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Useful Info

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Useful Info

Purpose of Alloying
 
The main purposes of adding alloying elements to steels can be listed as follows.
a) To improve hardening ability,
b) To increase hardness, strength and toughness,
c) To improve mechanical properties at low and high temperatures,
d) To increase the wear resistance,
e) To increase corrosion resistance,
f) To improve Magnetic Properties.
 
The effects of alloying elements on steel structure can be defined as follows.
 
Carbon (C): Provides strength and hardening ability. It reduces formability and weldability.
 
Chromium (Cr): It provides hardening depth, thermal strength, resistance to corrosion. Chromium is the basic alloying element of stainless steels.
 
Nickel (Ni): It has positive effects on hardening depth, ductility and thermal expansion. Increases the impact toughness of nickel and strength in annealed steels. Nickel is the second most important alloying element of austenitic stainless steels after chromium. The nickel content in austenitic stainless steels is between 7-20%.
 
Manganese (Mn): Increases strength, improves hardening depth, weldability and ductility. By binding with sulfur (S) (MnS), it prevents the brittleness (fragile FeS compound) caused by sulfur.
 
Silicon (Si): Improves high temperature resistance and magnetic properties; improves tensile strength and elasticity. It is included in steel as a deoxidizer.
 
Molybdenum (Mo): It provides thermal strength, temper brittleness, corrosion and abrasion resistance.
 
Vanadium (V): It provides thermal strength, resistance to tempering. It has a grain refining and carbide forming effect; increases the strength. Improves hardening ability.
 
Tungsten (W): It provides thermal hardness, resistance to tempering and abrasion resistance. It maintains hardness in rising temperature. Therefore, speed steels etc. are used.
 
Cobalt (Co): It is an alloying element used in alloyed tool steels. It is used to maintain the hardness of tool steels in hot. Provides abrasion resistance.
 
Titanium (Ti): It has a grain-reducing effect like vanadium. However, this effect is higher than that of vanadium.
 
Aluminium (Al): It is used to remove oxygen. It increases the yield strength and impact toughness. In addition, aluminum has a grain-reducing effect, it is the basic alloying element of nitriding steels. It is also used as a micro alloying element forming nitride and carbonitride in some micro alloy steels.
 
Lead (Pb): It decreases the rolling ability. It causes ruptures during rolling, negatively affects the surface quality. It increases the machining ability of steels, so it is used as an alloying element in free cutting steels.
 
Nitrogen (N): It is an undesirable element. It causes nitrogen brittleness, making its bending properties very bad.
 
Copper (Cu): It increases the yield and tensile strength, decreases the percent elongation and formability. Increases Corrosion resistance.
 
Tin (Sn): It does not affect the yield and tensile strength much, but creates problems in hot rolling.
 
Sulfur (S): It has little or no effect on yield and tensile strength. However, it has a great effect on the percentage elongation and toughness of the material. Sulfur significantly reduces the toughness and ductility of the material. Sulfur is an element in steel that remains from the production of steel and is removed from the structure as much as possible due to the above-mentioned undesirable properties. The sulfur content is kept high only in die cutting steels suitable for machining.
 
Phosphorus (P): Phosphor increases the yield and tensile strength of steel, worsens the percent elongation and bending properties too much, creates cold brittleness, and increases chip forming capability. Phosphorus is an element in steel that remains from production processes and is removed from the structure as much as possible due to its undesirable properties.
 
    Si Mn* Mn** Cr Ni* Ni** Al W V Co Mo S P  
Hardness ↓↓↓ ↑↑ ↓↓
Strength ↑↑
Yield Point ↑↑ ↑↑
Elongation ↑↑↑ ↑↑↑
Impact Resistance ↑↑↑ ↓↓↓
Elasticity ↑↑↑
Heat Resistance ↑↑↑ ↑↑↑ ↑↑ ↑↑ ↑↑
Cooling Speed ↓↓ ↓↓↓ ↓↓ ↓↓ ↓↓ ↑↑ ↓↓
Wear Resistance ↓↓↓ ↓↓ ↓↓ ↑↑↑ ↑↑ ↑↑↑ ↑↑
Forgability ↓↓↓ ↓↓↓ ↓↓ ↓↓ ↓↓↓ ↓↓↓
Machinability ↓↓↓ ↓↓↓ ↓↓ ↑↑↑ ↓↓↓
Tendency to Oxidize ↓↓ ↓↓↓ ↓↓ ↓↓ ↓↓ ↑↑ ↓↓
Corrossion Resistance ↑↑↑ ↑↑ ↑↑
↑ Increases   //   ↓ Decreases   //   ↔ Unchanges   //   – Has no effect or unknown effect   //
* Austenitic Steel   //   ** Perlithic Steel
 
  BRINEL HARDNESS VICKERS HARDNESS ROCKWELL C HARDNESS TENSILE STRENGTH   BRINEL HARDNESS VICKERS HARDNESS ROCKWELL C HARDNESS TENSILE STRENGTH   BRINEL HARDNESS VICKERS HARDNESS ROCKWELL C HARDNESS TENSILE STRENGTH  
HB HV HRC N/mm2 HB HV HRC N/mm2 HB HV HRC N/mm2
76.0 80 ── 265 233 245 21.3 785 (494) 520 50.5 1700
80.7 85 ── 270 238 250 22.2 800 (504) 530 51.1 1740
85.5 90 ── 285 242 255 23.1 820 (513) 540 51.7 1775
90.2 95 ── 305 247 260 24.0 835 (523) 550 52.3 1810
95.0 100 ── 320 252 265 24.8 850 (532) 560 53.0 1845
98.8 105 ── 335 257 270 25.6 865 (542) 570 53.6 1880
105 110 ── 350 261 275 26.4 880 (551) 580 54.1 1920
109 115 ── 370 266 280 27.1 900 (561) 590 54.7 1955
114 120 ── 385 271 285 27.8 915 (570) 600 55.2 1995
119 125 ── 400 276 290 28.5 930 (580) 610 55.7 2030
124 130 ── 415 280 295 29.2 950 (589) 620 56.3 2070
128 135 ── 430 285 300 29.8 965 (599) 630 56.8 2105
133 140 ── 450 295 310 31.0 995 (608) 640 57.3 2145
138 145 ── 465 304 320 32.2 1030 (618) 650 57.8 2180
143 150 ── 480 314 330 33.3 1060 ── 660 58.3 ──
147 155 ── 495 323 340 34.4 1095 ── 670 58.8 ──
152 160 ── 510 333 350 35.5 1125 ── 680 59.2 ──
156 165 ── 530 342 360 36.6 1155 ── 690 59.7 ──
162 170 ── 545 352 370 37.7 1190 ── 700 60.1 ──
166 175 ── 560 361 380 38.8 1220 ── 720 61.0 ──
171 180 ── 575 371 390 39.8 1255 ── 740 61.8 ──
176 185 ── 595 380 400 40.8 1290 ── 760 62.5 ──
181 190 ── 610 390 410 41.8 1320 ── 780 63.3 ──
185 195 ── 625 399 420 42.7 1350 ── 800 64.0 ──
190 200 ── 640 409 430 43.6 1385 ── 820 64.7 ──
195 205 ── 660 418 440 44.5 1420 ── 840 65.3 ──
199 210 ── 675 428 450 45.3 1455 ── 860 65.9 ──
204 215 ── 690 437 460 46.1 1485 ── 880 66.4 ──
209 220 ── 705 447 470 46.9 1520 ── 900 67.0 ──
214 225 ── 720 (456) 480 47.7 1555 ── 920 67.5 ──
219 230 ── 740 (466) 490 48.4 1595 ── 940 68.0 ──
223 235 ── 755 (475) 500 49.1 1630 ── ── ── ──
228 240 20.3 770 (485) 510 49.8 1665 ── ── ── ──
 
          The effect of the chemical composition of the welded part is very important in the concept of weldability. Especially Carbon (C) and Manganese (Mn) are the two most important elements that affect the hardening ability of unalloyed steel. In low alloy steels, in addition to Carbon and Manganese in the composition of the steel, alloying elements such as Chromium (Cr), Molybdenum (Mo), Vanadium (V), Nickel (Ni) and Copper (Cu) also contribute to hardness. Carbon Equivalent concept was created to determine the contribution of these elements to hardness. In this concept, the amount of carbon that gives the hardness equivalent to the hardness formed by the alloying elements in the composition of the steel is called Carbon Equivalent. The carbon equivalent formula (Ceq) adopted by the International Welding Institute's (IIW) Commission No. IX is as follows;
 
  Ceq = C + Mn + Cr+Mo+V + Ni+Cu  
6 5 15
 
          The formula given above can also be seen as a guide for the pre-annealing process, which is used to prevent rapid cooling of steels during welding. There is a relationship between carbon equivalent pre-annealing temperature roughly as follows.
 
  Carbon Equivalent (Ceq) (%) Pre-Annealing Temperature (ºC)  
0,45 < Ceq  There is no need for pre-annealing under normal atmospheric conditions.
0,45 ≤ Ceq ≤ 0,60  100 – 200
Ceq > 0,60 200 – 300
 
          As a result; When welding a steel, the first issue that comes to mind should be the chemical composition of the steel. The norm of the steel to be welded should be learned and the content and carbon equivalent should be determined from the chemical analysis tables in the steel certificate. Welding process should be done after checking the part thickness and deciding whether to apply a preheat according to the selected electrode diameter.
 
  Symbol Definition Symbol Definition  
+A (TC) Soft annealed +QT (TF) Quenched and tempered
+AC Spheroidized annealed +QW Quenched in water
+AR As rolled, natural state +RA Recrystallization annealing
+AT Solubilization annealed +S Annealed for cold shearing
+BC Hot formed and sandblasted +SR Stress relieved
+BK Bright down, no heat treatment after drawing +T Tempered
+BKW Cold drawing involving limited deformation +U Untreated
+C Cold-drawn +WW Hot forming
+CH Core hardenability +V Hardening and tempering
+CR Cold rolled HB General Brinell hardness, ball
+HC Hot rolled followed by cold hardening HV Vickers hardness
+H Normal hardenability at maximum range HR General Rockwell hardness
+HH Hardenability restricted towards top HRC Rockwell hardness, diamond penetrator
+HR Treated for a certain range of hardness …..E e.g. C45E with max sulphur content specified
+I Isothermal annealing …..R e.g. C45R with a range of sulphur content specified
+N (TD) Normalized …..K e.g. C15K, St 37-3 K = cold drawn
+NT Normalized and Tempered …K… e.g. CK15 = fully killed
+P Hardened by precipitation …m… e.g. Cm 55 with a range of sulphur content 0.020-0.040%
+PE Peeled X….. e.g. X6Cr17 X = the average content of at least one alloying element 5 %
+PL Polished (smoothed) …..J2 Guaranteed impact strength at –20°C > 40J
+Q Quenched …..J0 Guaranteed impact strength at 0°C > 27 J
+QA Quenched in air …..JR Guaranteed impact strength at +20°C > 27 J
+QO Quenched in oil …..G3 Fully killed steel
 

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