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IMPAIRMENT OF ASSETS (Details) R$ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2017 BRL (R$) | Dec. 31, 2016 BRL (R$) | Dec. 31, 2017 BRL (R$) segment | Dec. 31, 2016 BRL (R$) | Dec. 31, 2015 BRL (R$)
Impairment of assets |  |  |  |  |
Increase in discount rate |  |  | 0.50% |  |
Impairment of assets |  |  | R$ 1,114,807 | R$ 2,917,911 | R$ 4,996,240
Impairment of property, plant and equipment | R$ 265,369 | R$ 239,329 | 265,369 | 239,329 |
Impairment of goodwill |  |  | R$ 849,438 | R$ 2,678,582 | R$ 2,528,483
Number of operating segments | segment |  |  | 4 |  |
Period for projecting the cash flows for the goodwill impairment test |  |  | P5Y |  |
Discount rate |  |  |  |  |
Impairment of assets |  |  |  |  |
Sensitivity analysis, percent of increase | 0.50% | 0.50% | 0.50% | 0.50% |
Perpetuity growth rate |  |  |  |  |
Impairment of assets |  |  |  |  |
Sensitivity analysis, percent of decrease | 0.50% | 0.50% | 0.50% | 0.50% |
Property, plant and equipment |  |  |  |  |
Impairment of assets |  |  |  |  |
Recoverable amount |  | R$ 138,543 |  | R$ 138,543 |
North America |  |  |  |  |
Impairment of assets |  |  |  |  |
Impairment of property, plant and equipment | R$ 220,090 | 100,564 |  |  |
Impairment of goodwill | 849,438 |  |  | 2,678,582 |
Recoverable amount | R$ 849 | R$ 2,679,000 | R$ 849 | R$ 2,679,000 |
Perpetuity growth rate | 3.00% | 3.00% | 3.00% | 3.00% |
Pre-tax discount rate | 13.60% | 13.10% | 13.60% | 13.10% |
North America | Discount rate |  |  |  |  |
Impairment of assets |  |  |  |  |
Sensitivity analysis, amount above (below) book value | R$ (506,000) | R$ (872,000) | R$ (506,000) | R$ (872,000) |
North America | Perpetuity growth rate |  |  |  |  |
Impairment of assets |  |  |  |  |
Sensitivity analysis, amount above (below) book value | (310,000) | (661,000) | (310,000) | (661,000) |
South America |  |  |  |  |
Impairment of assets |  |  |  |  |
Impairment of property, plant and equipment |  | 138,765 |  |  |
Recoverable amount | R$ 437,000 | R$ 724,000 | R$ 437,000 | R$ 724,000 |
Perpetuity growth rate | 3.00% | 3.00% | 3.00% | 3.00% |
Pre-tax discount rate | 14.70% | 14.60% | 14.70% | 14.60% |
South America | Discount rate |  |  |  |  |
Impairment of assets |  |  |  |  |
Sensitivity analysis, amount above (below) book value | R$ 265,000 | R$ 486,000 | R$ 265,000 | R$ 486,000 |
South America | Perpetuity growth rate |  |  |  |  |
Impairment of assets |  |  |  |  |
Sensitivity analysis, amount above (below) book value | 318,000 | 561,000 | 318,000 | 561,000 |
Brazil |  |  |  |  |
Impairment of assets |  |  |  |  |
Impairment of property, plant and equipment | 45,279 |  |  |  |
Recoverable amount | R$ 1,747,000 | R$ 1,225,000 | R$ 1,747,000 | R$ 1,225,000 |
Perpetuity growth rate | 3.00% | 3.00% | 3.00% | 3.00% |
Pre-tax discount rate | 15.20% | 14.90% | 15.20% | 14.90% |
Brazil | Discount rate |  |  |  |  |
Impairment of assets |  |  |  |  |
Sensitivity analysis, amount above (below) book value | R$ 999,000 | R$ 425,000 | R$ 999,000 | R$ 425,000 |
Brazil | Perpetuity growth rate |  |  |  |  |
Impairment of assets |  |  |  |  |
Sensitivity analysis, amount above (below) book value | 1,254,000 | 673,000 | 1,254,000 | 673,000 |
Special Steel |  |  |  |  |
Impairment of assets |  |  |  |  |
Recoverable amount | R$ 3,989,000 | R$ 1,601,000 | R$ 3,989,000 | R$ 1,601,000 |
Perpetuity growth rate | 3.00% | 3.00% | 3.00% | 3.00% |
Pre-tax discount rate | 13.10% | 14.00% | 13.10% | 14.00% |
Special Steel | Discount rate |  |  |  |  |
Impairment of assets |  |  |  |  |
Sensitivity analysis, amount above (below) book value | R$ 3,422,000 | R$ 1,170,000 | R$ 3,422,000 | R$ 1,170,000 |
Special Steel | Perpetuity growth rate |  |  |  |  |
Impairment of assets |  |  |  |  |
Sensitivity analysis, amount above (below) book value | R$ 3,596,000 | R$ 1,301,000 | R$ 3,596,000 | R$ 1,301,000 |

X
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